Pancreatic cancer provides a major challenge to the managing physician both in terms of diagnosing the disease and subsequent treatment options. It is one of the most insidious forms of cancer. While being only the tenth most common form of cancer, with an estimated 32,000 new cases diagnosed in the U.S. annually, pancreatic cancer is the fourth and fifth leading cause of cancer deaths in men and women, respectively. At the present time gemcitabine (GEM) is considered the front-line, drug of choice for treatment of advanced pancreatic cancer. Although this agent can provide palliation of disease symptoms, it has not demonstrated a significant survival advantage. We have observed that in vitro, pancreatic cancer cells respond to increasing doses of GEM by undergoing apoptosis. However, even at GEM concentrations as high as 100 times the IC50, a significant fraction of cells do not undergo apoptosis, but instead, are induced to enter a senescence-like state. Senescence is characterized by cell cycle arrest in and mitotic inactivity. However, senescent cells are still viable and, in vivo, may represent a population of cells from which the tumor could re-grow or may provide for the production of factors necessary for tumor growth. Reducing the number of senescent cells after chemotherapy will likely reduce the number of tumor progenitor ("stem") cells and the production of pro-growth factors. Bioactive sphingolipids, and in particular ceramide, provide important signals for the induction of apoptosis, but are also able to induce a senescence-like phenotype. Specific modulation of intracellular levels of sphingo- lipids may provide a means to direct cells preferentially into either senescence or apoptosis. We have reported that, by addition of sphingomyelin at non-toxic levels in the culture media, pancreatic cancer cells, which normally undergo senescence when treated with GEM, preferentially enter into apoptosis. Therefore, we hypothesize that the bio-availability of ceramide (and/or sphingomyelin) is critical to the choice of whether the cell follows a pathway towards apoptosis or senescence, as a consequence of exposure to GEM. The aims of this proposal are to evaluate the mechanism by which modulation of bioactive sphingolipids affects the decision between apoptosis and senescence with the goal that this knowledge will enhance our understanding of cellular stress response mechanisms. It is anticipated that this knowledge will lead to more effective management of pancreatic cancer. Specifically, we will use pancreatic cancer as a model to examine the association of specific sphingolipids and sphingolipid biosynthetic enzymes with the induction of apoptosis and senescence and examine the nature of sphingolipid-mediated modulation of gene and protein expression and activity associated with induction of apoptosis and senescence in multiple cell lines and in vivo.Project Narrative Bioactive sphingolipids provide important signals for the induction of apoptosis, but are also able to induce a senescence-like phenotype. We have reported that, exogenous sphingomyelin induces pancreatic cancer cells, which normally undergo senescence when treated with gemcitabine, to preferentially enter into apoptosis. Therefore, we hypothesize that the bio-availability of sphingolipids is critical to the choice of whether the cell follows a pathway towards apoptosis or senescence. This application proposes to evaluate the mechanism by which modulation of bioactive sphingolipids affects the decision between apoptosis and senescence with the goal that this knowledge will enhance our understanding of the cellular stress response and lead to improved anti-cancer therapies.